short circuit

[jcb]

Tail light circuit has a dead short, blows fuse. With no fuse in place If I short across the switch, power to tail light circuit, it goes to ground. Am I correct that the short is somewhere between the switch and the fuse.

I have traced the loom to the rear and can seen no area that looks to be damaged. Everything was fine and suddenly a dead short. Any suggestions are very much appreciated. Thanks. JB

[SteveJ]

There are several points where you can break the circuit.

HOWEVER, before you do that, check all of the sockets on that side for corrosion. That is very common on our old cars. Clean out the corrosion as needed and coat with dielectric grease to reduce the chances of it coming back.

After that go to the FSM. Look in the BE section, especially focusing on BE-10. That breaks down the circuit and gives you an idea of where all of the connections are.

Please use an ohmmeter to find the short. Jumpering out the fuse can cause an electrical fire.

The way short circuits typically develop (not all inclusive):

1. Corrosion in the sockets

2. Bad rewiring

3. Rubbing or other degredation in the insulation (Other degredation can include heat from the environment or electrical current.)

4. Working on another component and damaging the wiring.

[jcb]

Steve, I was glad to see you answer as you always give good advice. I have worked on the interior, seats, carpet,ect., but do not feel like I could have damaged any wiring. I will check on the BE section of the FSM and look for corrosion. Will let you know when and where I find the short. Thanks again, JB

[SteveJ]

I'm glad you like my advice. I'm full of it...Hmm, that didn't sound right.

Anyway, if it's not corrosion, I suggest a divide and conquer approach for narrowing down a short. Break the circuit into three sections: front, back and dash. That would be at connector C-3 and at the turn signal switch. Test each of them for a short by checking resistance from the positive side of the circuit to the chassis ground. Take the bulbs out to prevent false positives. Report the resistance readings if it's not obvious where you should go next.

[Mikes Z car]

I am ignorant about 280Z wiring but if the tailight circuit is the same as the side marker light circuit, remember that thing where on a 240Z the side marker light socket would short? Can that happen on a 280Z?

[SteveJ]

Mike, thanks for adding your input. I totally misread the initial post. Yes, the side markers are part of the taillight circuit. Somehow I got it into my head he was talking about the turn signals. If it is the parking lights, that is on page BE-13.

[jcb]

Thanks Mike and Steve. Yes I'm working on the tail light, side marker light circuit. I am trying to isolate the short to one section of the circuit. It turned cold this afternoon and I got cold and frustrated and decided to wait for better weather and a better mood. Mike, I will check the side marker sockets first. Again I don't know when this happened as I have not driven at night. Only checked on the lights as I need to get a safety inspection sticker. Last thing I knew every thing was working. Will let you know and thanks again. JB

[LeonV]

That's a good idea. Check all sockets, starting with the parking lights. Those are a very likely culprit.

[jcb]

Hey Steve,Mike ,Leon, I found it but I will never disclose the stupid thing I had done to cause the direct ground. No one should be this dumb. Thanks for all your help. I really enjoy this forum and learning about Z cars. JB

[LeonV]

Hey Steve,Mike ,Leon, I found it but I will never disclose the stupid thing I had done to cause the direct ground. No one should be this dumb. Thanks for all your help. I really enjoy this forum and learning about Z cars. JB

Good job! You never know, maybe it'll help the next guy. It's always nice to hear the solution, even if it's from a silly mistake.

Besides, the worst that can happen is that we taunt you a wee little bit.

Edited April 15, 2013 by LeonV

[mlc240z]

No, the worst that can happen is if you don't go away, we will taunt you a second time.......

That was for you, LeonV (from one old Python fan to another)

jcb, please share. We've all been guilty of some bonehead 'duh' moments. You'd be surprised how many people will say, 'yea, I did that once too.'

Think of it as a public service.

[SteveJ]

Hey Steve,Mike ,Leon, I found it but I will never disclose the stupid thing I had done to cause the direct ground. No one should be this dumb. Thanks for all your help. I really enjoy this forum and learning about Z cars. JB

Oh come on. That's part of the sharing process. Heck, I once burned up a wiring harness when I forgot to secure a battery properly. Most of us have done something bone-headed to our cars. It's more of an issue of whether or not it came back to bite us.